The day after having unprotected sex I took the plan b pill, 5 days later I started spotting light red/pink, is this implantation bleeding?

Probably not. The plan B pill is a high dose of progesterone which makes your uterine lining incompatible with a potential embryo. That high dose of progesterone can also cause your lining to be more friable and likely to bleed. It's very common to have irregular spotting when you take plan B. Less likely to be implantation bleeding.